1. Field of the Invention
The present invention relates to a new and improved method of preparation of trialkyl tetrathiophosphates.
2. The Prior Art
Tetrathiophosphates have been prepared in the prior art by reacting lead thiolates with thiophosphoryl chloride according to the following general reaction scheme: EQU Pb(SR).sub.2 + P(S)Cl.sub.3 .fwdarw. (RS).sub.3 P(S)+ R.sub.2 S.sub.2 + PbCl.sub.2 ( 2)
wherein R is selected from the group consisting of CH.sub.3, C.sub.2 H.sub.5, n-C.sub.4 H.sub.9, o-CH.sub.3 C.sub.6 H.sub.4, p-CH.sub.3 C.sub.5 H.sub.4 and p-ClC.sub.6 H.sub.4. Under reaction (2), trialkyl tetrathiophosphates are prepared in boiling benzene whereas triaryl tetrathiophosphates can only be obtained in boiling xylene.
Another reaction is observed for thiolates, namely: EQU Pb(SR).sub.2 + P(S)Cl.sub.3 .fwdarw. PbS+ R.sub.2 S.sub.2 + PCl.sub.3 ( 3)
wherein R is selected from the group consisting of CH.sub.2 C.sub.6 H.sub.5, C.sub.6 H.sub.5, m--CH.sub.3 C.sub.6 H.sub.4. These reactions are described in Phosphorus, R. A. Shaw and M. Woods, Vol. 1, Part 1, (Oxford, England, 1971) p. 42.
Other known methods of preparing tetrathiophosphates include the reaction of thiophosphoryl chloride with either a thiol or a sodium thiolate and the reaction of phosphorus pentasulfide and thiols.